Fix port 5000 conflict and nginx MIME type warnings

- frontend.py: read PORT env var instead of hardcoding 5000
(entrypoint starts frontend with PORT=5003, so dashboard keeps 5000)
- nginx.conf: remove sub_filter_types text/html from /fix/ and /frontend/
blocks — text/html is nginx sub_filter default, explicit declaration
caused duplicate MIME type warnings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/frontend.py

@@ -87,7 +87,8 @@ def trades():
     return (r.text, r.status_code, {'Content-Type': 'application/json'})
 
 if __name__ == '__main__':
-    app.run(host='0.0.0.0', port=5000)
+    port = int(os.getenv('PORT', '5000'))
+    app.run(host='0.0.0.0', port=port)
 
 
 @app.route('/submit', methods=['POST'])

nginx.conf

@@ -28,7 +28,6 @@ http {
             sub_filter         'href="/'    'href="/frontend/';
             sub_filter         'action="/'  'action="/frontend/';
             sub_filter_once    off;
-            sub_filter_types   text/html;
             proxy_redirect     / /frontend/;
         }
 
@@ -41,7 +40,6 @@ http {
             sub_filter         'href="/'    'href="/fix/';
             sub_filter         'action="/'  'action="/fix/';
             sub_filter_once    off;
-            sub_filter_types   text/html;
             # Rewrite Location headers on Flask redirects
             proxy_redirect     / /fix/;
         }